Such mat switches are used, for instance, as protection devices for closers. When an object, located in the path of contact closing edges, is in contact with the mat switch, a closed path, similar to that of a turned-on switch is established, through which a safety measure, as a rule a disconnection of the drive for the closer, can be initiated. Such mats are also used as contact floor mats within the path of the closing edges, so that the drive can not be actuated, as long as a person stands on the contact floor mat.
A mat of this kind is known from the publication "THE SAE JOURNAL OF AUTOMOTIVE ENGINEERING" Vol. 79, No. 10, Oct. 1091, page 22 and serves there as a sensor indicating whether the seat of a vehicle is occupied or not. The contact surfaces consist of thin copper sheet, and the bulges are formed therein by impression. The shape-preserving rigidity of these sheets required by the impression results however in the need for relatively high forces in order to establish contact. In addition, the acting forces have to be distributed over a relatively large surface, in order to counteract the high shape-preserving rigidity of the contact surfaces, to bring them closer to each other and establish contact between them. If the mat switch is subjected only to a local pressure, no contact may be made as a result of these forces, while when bigger forces are applied there can result a permanent deformation of the contact surface.
A similar mat switch is also known from the German open application DE-OS No. 24 18 856. However, there the bulges within the range of the contact windows are formed in the opposite direction, so that in the window area the contact surfaces are separated from each other by a greater distance than in the area of the spacers. When pressure is applied, the bulges reverse themselves elastically towards the opposite contact surface and establish the contact this way. But, even in this case, considerable forces are required, since the contact surfaces must have a sufficient shape-preserving rigidity. Also, the mat switch must be sealed in a synthetic-material sheathing, for the purpose of avoiding the penetration of dirt or water.
In the mat switch known from the German published specification DE AS No. 11 69 001, the contact surfaces are flat and parallel when not subjected to a load. The upper surface to be exposed to the load is made of heavy sheet metal, resistant to any bending, while the lower contact surface is made of relatively light sheet metal. The lower contact surface is provided at its bottom with base projections, arranged in the area of the contact windows. When the mat switch is subjected to load, the base projections push the lower contact surface upwardly, in the area of the contact windows and the contact is established. Here too, considerable forces are required in order to initiate the switching operation, because deformation of the entire lower contact surface required, due to the rigidity of the upper contact surface.
Finally, a process for manufacturing a mat switch is known from U.S. Pat. No. 3,722,086, wherein at first spacers are fastened to one plate-like contact surface and an O-ring is superimposed along the edges. A second contact plate is laid on top thereof and the inner space is evacuated through an opening. As a result, the two contact plates come to rest one against the other, between the spacers. After a polymer ribbon is wound around the two plates, they are both suspended in a mold. After that the inner space is aerated through a hollow needle, the contact plates resume their original flat shape, plane-parallel with respect to each other, which causes the enveloping mold to assume a wave-like structure on the outside.
The enveloping mold has therefore, in the area of the contact windows, a greater thickness and forms, there too, projections through which the two contact surfaces come to lie against each other. This way, the two contact surfaces have a high degree of shape-preserving rigidity also in this case, so that contact is established only when relatively high pressure forces act upon the mat switch.
These known set-ups are therefore suited only to sense such pressure forces like the ones initiated by the body weight of a person. They are, for this reason, not suited for use on strip switches which respond already to very low pressure forces, like for instance the ones used on closing devices.